Speech neuroprosthesis: revision 3 to 4

Revision 3

Revision 4

type: "technology"

status: "experimental"

horizon: "2030s"

trl: 5

trl: 6

categories: ["cybernetics"]

tags: ["bci", "speech decoding", "als", "anarthria", "neural decoding", "communication"]

summary: "A brain-computer interface that reconstructs intended speech from motor cortex activity, producing text or synthesized voice for people who cannot speak."

summary: "A brain-computer interface that reconstructs intended speech from motor cortex activity, producing text or synthesized voice for people who cannot speak."

updated: "2026-10-29"

updated: "2026-10-30"

humanEvidence: "Published results come from one or a few implanted participants, mostly with ALS or brainstem stroke; no multi-participant efficacy trial has been run and no device is approved anywhere."

humanEvidence: "Peer-reviewed results come from single implanted participants or groups of up to four, mostly with ALS or brainstem stroke; one man has used a system at home for nearly two years, and no efficacy trial has reported."

access: "Not obtainable: a handful of research implants at academic centres under investigational device exemptions, with no approved or purchasable system."

access: "Not obtainable: research implants at academic centres and in small company feasibility studies, all investigational, with no approved or purchasable system as of October 2026."

reversibility: "difficult"

issues: ["Neuralink's 75 wpm figure rests on a company post about a paywalled conference abstract that was not read directly.", "Paradromics' September 2026 speech claims are sourced only to a local news report with no speed figure."]

---

```infobox

{ "label": "First sentence decoding", "value": "2021" },

{ "label": "Best reported rate", "value": "~60-80 words per minute" },

{ "label": "Participants per study", "value": "One to a few" },

{ "label": "Company trials", "value": "Neuralink, Paradromics (from 2025)" },

{ "label": "Regulatory status", "value": "Investigational" }

]

}

retain the intention and the neural machinery for speech but have lost the motor pathway: those with

amyotrophic lateral sclerosis, brainstem stroke, or severe anarthria from other causes. Between 2021

and 2025 the field moved from decoding a fifty-word vocabulary at a conversational crawl to

near-real-time output over vocabularies of a hundred thousand words.

near-real-time output over vocabularies of a hundred thousand words. By 2026 one participant had used

such a system at home for nearly two years, and two companies had begun small feasibility trials of

fully implanted wireless versions.

These systems decode attempted articulation rather than thought. The signals come from the region of

cortex that would drive the lips, jaw, tongue and larynx. The decoder recovers a motor plan, and

[

  { "value": "~15 wpm", "label": "First sentence decoding", "note": "2021, 50-word vocabulary, roughly a quarter of words wrong" },

  { "value": "~15 wpm", "label": "First sentence decoding", "note": "2021, 50-word vocabulary, roughly a quarter of words wrong" },

{ "value": "62 wpm", "label": "Penetrating-array result", "note": "2023, Stanford, 125,000-word vocabulary" },

{ "value": "78 wpm", "label": "Surface-array result", "note": "2023, UCSF, with synthesized voice and avatar" }

{ "value": "78 wpm", "label": "Surface-array result", "note": "2023, UCSF, with synthesized voice and avatar" },

{ "value": "56 wpm", "label": "Average rate in home use", "note": "2026 report, one man with ALS, nearly two years" }

]

```

Speech production has a somatotopic map. Along the ventral part of the precentral gyrus, cortical

populations encode the movements of individual articulators, and this organization persists in

people who have been unable to speak for years; the map does not disappear when the output pathway

people who have been unable to speak intelligibly for years; the map does not disappear when the output pathway

fails. The whole field depends on that persistence.

fails.[^willett2023] The whole field depends on that persistence.

A speech neuroprosthesis records from that cortex and extracts features: high-gamma power for

[[ecog-interfaces]], or threshold crossings and band power for a penetrating [[utah-array]]. It

used for cursor control, applied to a much higher-dimensional output space.

> [!key] The language model does a lot of the work

> Raw phoneme decoding accuracy is well below the headline word accuracy. A substantial share of

> Raw phoneme decoding is error-prone, with about one phoneme in five wrong in the 2023 Stanford

> performance comes from the language model choosing the most probable sentence consistent with a

> system, and the language model often corrected those errors to recover the intended word.[^willett2023]

> noisy neural signal. This is legitimate engineering, and human listeners do the same thing. It

> A substantial share of performance comes from the language model choosing the most probable

> does mean that the reported word error rate is a property of the whole system, and that unusual or

> sentence consistent with a noisy neural signal. This is legitimate engineering, and human listeners

> unpredictable utterances are decoded worse than the aggregate figure suggests.

> do the same thing. It does mean that the reported word error rate is a property of the whole

> system, and that unusual or unpredictable utterances are decoded worse than the aggregate figure

> suggests.

## Development history

97.5 percent word accuracy over a 125,000-word vocabulary, sustained across 8.4 months in a

participant with ALS, with the system usable from the first session. In self-paced conversation the

rate was about 32 words per minute over more than 248 cumulative hours, slower than either 2023

result.[^card2024] Later work has gone after latency, with streaming architectures that emit words

result.[^card2024] Later work went after latency. The UCSF group built a streaming decoder that

as they are formed rather than at the end of a sentence, and voice synthesis fast enough to preserve

synthesizes speech in the participant's pre-injury voice in 80-millisecond increments rather than at

conversational turn-taking and some prosody.[^littlejohn2025]

the end of a sentence.[^littlejohn2025] The UC Davis group, working with the same man as the 2024

report, synthesized voice from intracortical activity within 10 milliseconds and decoded enough

paralinguistic information for him to change intonation and sing short melodies. Naive listeners

transcribing that synthesized voice still got a median of about 44 percent of words wrong, against

roughly 96 percent for his own dysarthric speech.[^wairagkar2025]

In 2026 the same UC Davis team reported long-term independent home use. Over nearly two

years the participant used the system for more than 3,800 hours at home with no researchers present,

communicating about 1.96 million words at an average of 56 words per minute and holding a full-time

job. He rated 92 percent of sentences as at least mostly correct, a self-report the authors note

they could not check against ground truth; in formal tests word accuracy stayed above 99 percent on

a 125,000-word vocabulary.[^card2026]

A related line uses imagined handwriting instead of speech. Decoding attempted pen strokes from

motor cortex produced roughly 90 characters per minute in one participant. That remains the fastest

motor cortex produced roughly 90 characters per minute in one participant, faster than any earlier

character-level result, and it shows that the choice of imagined movement is itself a design

brain-computer interface typing result, and it shows that the choice of imagined movement is itself

parameter.[^willett2021]

a design parameter.[^willett2021]

## Company trials

Two companies opened early feasibility studies of fully implanted wireless speech devices:

[[neuralink|Neuralink]]'s began in October 2025, and Paradromics' was approved in November 2025 and implanted

its first participant in June 2026.

Neuralink's study, VOICE, tests the skull-mounted N1 implant, whose electrode threads

are placed by the company's R1 robot. Registered with ClinicalTrials.gov, it started on 3

October 2025 at UT Southwestern Medical Center in Dallas, with a registered target of six adults

with severe speech impairment and impaired upper-limb function from ALS, primary lateral sclerosis,

stroke or spinal cord injury. Its primary outcomes are device- and procedure-related adverse events

at twelve months; efficacy is a secondary outcome measured as the monthly maximum of correct words

per minute. The registry lists "Telepathy" among the implant's other names.[^voice2025] In May 2025

Neuralink announced that the US Food and Drug Administration had granted the speech device a

breakthrough device designation, a programme meant to speed development and review that does not

amount to approval.[^reuters2025]

Neuralink's trial page says participants attempt or imagine speaking, with output as text or a

re-created voice, and that its median participant decodes about 50 words per

minute.[^neuralinkspeech] On 28 October 2026 the company

stated that one participant with ALS reached 75 words per minute with a 5.8 percent word error rate

on a 125,000-word vocabulary in the first week, citing a conference abstract presented at the

Northeast ALS Consortium meeting.[^neuralinkneals2026] Those figures have not appeared in a

peer-reviewed paper. A blog post the next day described features built during a 72-hour visit

to one participant's home, among them decoding that starts and stops without a button press and

synthesized speech fed into phone calls.[^neuralinkhack2026]

Paradromics received approval for an investigational device exemption in November 2025 for

Connect-One, a feasibility study of its Connexus device that initially enrols two participants

across sites at UC Davis, Massachusetts General Hospital and the University of

Michigan.[^paradromics2025] The study's first implant took place at Michigan in June 2026, in a woman with

motor neuron disease; the device has 421 microelectrodes connected to a transceiver in the

chest.[^michigan2026] In September 2026 the company said she had used it for real-time text and

synthesized speech, but the report gave no speed figure; its only accuracy claims were the company's

statements that selected sentences were decoded without error, and it cited no

publication.[^cbsaustin2026]

> [!debate] Musk's bandwidth forecast

> Elon Musk wrote on 30 October 2026 that Neuralink's first product, Telepathy, "enables high-speed

> communication with computers or humans simply by thinking" and that its "[o]utput bandwidth will

> vastly exceed the fastest human speech or typing in a few years."[^musk2026] In the speech study

> his post quotes, the implant decodes attempted or imagined speech from speech motor cortex, not

> thought in general.

> Natural conversation runs at roughly 150-160 words per minute.[^willett2023][^neuralinkspeech]

> Peer-reviewed decoding has reached a median 78 with a quarter of words wrong,[^metzger2023] the

> longest home use averaged 56,[^card2026] and Neuralink gives its own median participant about

> 50,[^neuralinkspeech] so matching ordinary conversation would take roughly a two- to threefold

> gain, and exceeding the fastest speakers more than that; no published result shows either. The trial behind the post lists safety, not speed, as its primary outcome.

## What has and has not been shown

The published work has shown fluent, large-vocabulary decoding in individual participants,

performance stable enough for daily use over months, and voice synthesis with recognisable identity.

It has shown decoding from both surface and penetrating electrodes, and in at least one case usable

results from the first day of calibration.

results from the first day of calibration. In one man it has shown nearly two years of independent

home use.[^card2026]

None of this has been shown in more than a handful of people. Nearly every result above comes from a

single participant, and participants differ in implant site, disease stage and residual

capabilities. There is no multi-participant efficacy trial and no approved device. There are no data

capabilities. There is no multi-participant efficacy trial and no approved device. The only long-term

on how the systems perform in noisy real-world settings with fatigue and changing medication, and

home data come from one participant; the authors name the single participant as a limitation and note

almost no work outside English. Most systems remain tethered through a percutaneous connector to

that they did not systematically assess fatigue.[^card2026] There are still almost no data on noisy

laboratory hardware.

settings or changing medication. Most work remains in English, although

one team decoded both Spanish and English from a bilingual participant[^silva2024] and a Chinese

group decoded Mandarin syllables, tones included, in real time.[^qian2025] The system with the longest record of

independent home use connects through percutaneous wired connectors to research computers that trained care

partners set up each day.[^card2026]

These decoders also address only speech *production*. They do not help people whose language

comprehension or formulation is impaired, which excludes many stroke and dementia patients. A

and hard to evaluate, precisely because they have no equivalent of a transcript to score.

> [!caution] Every headline figure is one person's decoder

> The 2021, 2023 and 2024 results each come from a single implanted participant. The largest group

> The 2021, 2023, 2024 and 2026 results each come from a single implanted participant. The 2025

> in any speech-decoding paper is the four BrainGate2 participants (T12, T15, T16 and T17), reported

> inner-speech study analysed four BrainGate2 participants (T12, T15, T16 and T17).[^kunz2025]

> together in 2025.[^kunz2025] Each decoder is trained on that individual's own attempted speech and

> The decoders behind those results were each trained on one person's own attempted speech. Models

> does not transfer. Models trained jointly across participants have appeared only recently, and

> trained across people are newer: a 2026 reanalysis of two public datasets aligned each person's cortex into

> they still align each new person's cortex into the shared space with a per-subject

> a shared space with a per-subject transform,[^boccato2026] and a 2026 preprint that pooled six

> transform.[^boccato2026] BrainGate2 is a registered feasibility study, so the published figures

> intracortical participants reported that a shared model beat every individual one and adapted to a

> describe individuals rather than a cohort, and there is no denominator for how often an implant

> new user from fewer than 200 sentences, reaching a word error rate below 7 percent.[^fogg2026] BrainGate2 is a pilot clinical trial and the

> reaches conversational performance. A trial that reported performance for every participant it

> company studies are early feasibility studies, so the published figures describe individuals

> enrolled would supply one.

> rather than a cohort, and there is no denominator for how often an implant reaches conversational

> performance. A trial that reported performance for every participant it enrolled would supply one.

## Inner speech and privacy

The obvious worry is that a device might transcribe thoughts a person did not choose to utter. That

is neither science fiction nor imminent. Attempted speech and imagined speech produce overlapping

but distinguishable patterns in motor cortex. A 2025 study reported that imagined speech can be

but distinguishable patterns in motor cortex. A 2025 study decoded instructed inner speech from the

decoded from the same electrodes, and also demonstrated a keyword-gated mode in which the decoder

same electrodes with word error rates of 26-54 percent on a large vocabulary, but could not decode

ignores neural activity until the user internally produces a chosen password.[^kunz2025]

complete, intelligible sentences during free-form thinking. It also demonstrated a keyword-gated

mode in which the decoder stays locked until the user imagines saying a rare word,

"chittychittybangbang"; in real-time tests with one participant the keyword was correctly detected

or correctly ignored 98.75 percent of the time.[^kunz2025]

That is a reassuring engineering answer to a real problem, and it shows the shape of the issue: the

safeguard has to be designed in, because the signal is present whether or not the system is asked to

use it. The broader questions belong to [[mental-privacy]] and the developing [[neurorights]]

frameworks. They include who holds the neural recordings, whether decoded text has legal status as

frameworks. The ethicist Marcello Ienca places speech decoding within the narrow sense of mental

speech, and what happens when a decoder outputs a sentence the user did not intend. Error correction

privacy, the decoding of present thoughts, which he distinguishes from inferences about traits and

in a speech prosthesis matters for more than appearance, because a wrong word attributed to a person

risks drawn from brain data.[^ienca2026] The questions include who holds the neural recordings, whether decoded text has legal status as speech,

who cannot verbally repudiate it is a distinctive harm.

and what happens when a decoder outputs a sentence the user did not intend. Error correction in a

speech prosthesis matters for more than appearance, because a wrong word attributed to a person who

cannot verbally repudiate it is a distinctive harm.

## Outlook

The near-term path is a pivotal trial in ALS, the population with the clearest need and the

The company studies are early feasibility trials, the stage before any pivotal trial, and both

strongest existing results, using a fully implanted wireless system rather than a percutaneous one.

enrol people with ALS among other causes of severe paralysis, the population with the clearest need and the strongest existing

Progress there depends less on decoding accuracy, which is already adequate, than on hardware

results.[^voice2025][^paradromics2025] Progress there arguably depends less on decoding accuracy,

longevity, surgical throughput, and the unglamorous work of making a device that a clinician can

which the academic results suggest is already adequate for conversation, than on hardware longevity,

implant and a family can support at home. The same constraints shape every implanted

surgical throughput, and the unglamorous work of making a device that a clinician can implant and a

[[brain-computer-interface]], from the endovascular [[stentrode]] to the penetrating threads of

family can support at home. The same constraints shape every implanted

[[neuralink]].

[[brain-computer-interface]], from the endovascular [[stentrode]] of [[synchron]] to the penetrating

threads of Neuralink.

These systems are also the strongest existing evidence for the modest version of

[[human-ai-merger]]. A machine-learning model sits between cortex and the world, doing inferential

work that the user's damaged nervous system cannot, and the user cannot tell their own contribution

work that the user's damaged nervous system cannot, and the output does not separate the user's

from the model's.

contribution from the model's.

The scientific question underneath is how much of language can be reached this way at all. Decoding

articulation works because articulation is motor. Semantic content, the words a person has not yet

[^littlejohn2025]: `paper` Littlejohn, K. T. et al. "A streaming brain-to-voice neuroprosthesis to restore naturalistic communication." *Nature Neuroscience*, 2025.

[^littlejohn2025]: `paper` Littlejohn, K. T. et al. "A streaming brain-to-voice neuroprosthesis to restore naturalistic communication." *Nature Neuroscience*, 2025.

[^kunz2025]: `paper` Kunz, E. M. et al. "Inner speech in motor cortex and implications for speech neuroprostheses." *Cell*, 2025. {The password-gated mode is a laboratory demonstration in already implanted research participants, not a safeguard validated in any deployed device.}

[^wairagkar2025]: `paper` Wairagkar, M. et al. "An instantaneous voice-synthesis neuroprosthesis." *Nature* 644, 145-152, 2025. https://doi.org/10.1038/s41586-025-09127-3

[^boccato2026]: `paper` Boccato, T., Olak, M. and Ferrante, M. "Cross-subject decoding of human neural data for speech brain–computer interfaces." *Journal of Neural Engineering*, 2026. {A reanalysis of the two largest public intracortical speech datasets, so its own sample is four participants; the authors name that as the study's fundamental limitation.}

[^card2026]: `paper` Card, N. S. et al. "Long-term independent use of an intracortical brain-computer interface for speech and cursor control." *Nature Medicine* 32, 2504-2510, 2026. https://doi.org/10.1038/s41591-026-04414-6 {One participant, T15; the 92 percent figure is his own rating of his sentences, which the authors could not verify independently.}

[^kunz2025]: `paper` Kunz, E. M. et al. "Inner speech in motor cortex and implications for speech neuroprostheses." *Cell*, 2025. {The keyword lock was tested in real time with one already implanted participant, T12; it is a laboratory demonstration, not a safeguard validated in any deployed device.}

[^boccato2026]: `paper` Boccato, T., Olak, M. and Ferrante, M. "Cross-subject decoding of human neural data for speech brain computer interfaces." *Journal of Neural Engineering*, 2026. {A reanalysis of the two largest public intracortical speech datasets, so its own sample is four participants; the authors name that as the study's fundamental limitation.}

[^fogg2026]: `preprint` Fogg, Z. M. et al. "A generalizable speech neuroprosthesis." *bioRxiv*, 2026. https://doi.org/10.64898/2026.07.23.739430

[^silva2024]: `paper` Silva, A. B. et al. "A bilingual speech neuroprosthesis driven by cortical articulatory representations shared between languages." *Nature Biomedical Engineering* 8, 977-991, 2024. https://doi.org/10.1038/s41551-024-01207-5

[^qian2025]: `paper` Qian, Y. et al. "Real-time decoding of full-spectrum Chinese using brain-computer interface." *Science Advances* 11, eadz9968, 2025. https://doi.org/10.1126/sciadv.adz9968 {Several authors are employees of Neuroxess, the company that supplied the implant used in the study.}

[^ienca2026]: `paper` Ienca, M. "Two kinds of mental privacy: what speech decoding does and does not threaten." *Hastings Center Report* 56(5), 25-27, 2026. https://doi.org/10.1002/hast.70116

[^voice2025]: `trial` Neuralink Corp. "VOICE: An Early Feasibility Study of a Precise Robotically Implanted Brain-Computer Interface for Communication Restoration." ClinicalTrials.gov NCT07224256, first posted 4 November 2025. https://clinicaltrials.gov/study/NCT07224256

[^reuters2025]: `news` Reuters. "Neuralink's speech restoration device gets FDA's 'breakthrough' tag." 5 May 2025, syndicated by Tuoi Tre News. https://news.tuoitre.vn/neuralinks-speech-restoration-device-gets-fdas-breakthrough-tag-103250505161133851.htm

[^neuralinkspeech]: `statement` Neuralink. "Speech Restoration." Clinical trials page, accessed 30 October 2026. https://neuralink.com/trials/speech-restoration/

[^neuralinkneals2026]: `statement` Neuralink. Post on X reporting early speech restoration data, 28 October 2026. https://x.com/neuralink/status/2115534593147187397 {A company summary of a conference abstract, not a peer-reviewed paper; the figure is one participant's first-week result.}

[^neuralinkhack2026]: `statement` Neuralink. "A 72-Hour Engineering Sprint for Translating Thought to Speech." Company blog, 29 October 2026. https://neuralink.com/updates/72-hour-voice-hackathon/

[^musk2026]: `statement` Musk, E. Post on X quoting Neuralink's hackathon thread, 30 October 2026. https://x.com/elonmusk/status/2116018780111597911

[^paradromics2025]: `statement` Paradromics. "Paradromics Receives FDA Approval for the Connect-One Clinical Study with the Connexus Brain-Computer Interface." Press release, 20 November 2025. https://paradromics.com/news/paradromics-receives-fda-approval-for-the-connect-one-clinical-study-with-the-connexus-brain-computer-interface/

[^michigan2026]: `statement` Michigan Medicine. "University of Michigan implants first-in-human Paradromics wireless brain-computer interface, designed to restore communication." News release, 17 June 2026. https://www.michiganmedicine.org/news-release/university-michigan-implants-first-human-paradromics-wireless-brain-computer-interface-designed

[^cbsaustin2026]: `news` Maciborski, W. "'I have a lot to say': Austin brain implant helps patient communicate in real time." CBS Austin, 14 September 2026. https://cbsaustin.com/news/local/i-have-a-lot-to-say-austin-brain-implant-helps-patient-communicate-in-real-time {The report relies on the company and the implanting surgeon and quotes no independent expert.}